Agfdhyk

I'm working with Tokio doing some UDP stuff.

I want to record the amount of time my UDP probe future takes to resolve. I came up with the following function, time_future(), to wrap a future and give me the result and a duration. The function seems very naive and I think Rust has the power to express the concept much more cleanly.

My working code (Playground):

extern crate futures; // 0.1.25

extern crate tokio; // 0.1.11



use std::time::{Duration, Instant};



use futures::future::{lazy, ok};

use futures::Future;

use tokio::runtime::current_thread::Runtime;

use tokio::timer::Delay;



struct TimedFutureResult<T, E> {

    elapsed: Duration,

    result: Result<T, E>,

}



impl<T, E> TimedFutureResult<T, E> {

    pub fn elapsed_ms(&self) -> i64 {

        return (self.elapsed.as_secs() * 1000 + (self.elapsed.subsec_nanos() / 1000000) as u64)

            as i64;

    }

}



fn time_future<F: Future>(f: F) -> impl Future<Item = TimedFutureResult<F::Item, F::Error>> {

    lazy(|| {

        let start = Instant::now();



        f.then(move |result| {

            ok::<TimedFutureResult<F::Item, F::Error>, ()>(TimedFutureResult {

                elapsed: start.elapsed(),

                result: result,

            })

        })

    })

}



fn main() {

    let when = Instant::now() + Duration::from_millis(100);



    let f = time_future(Delay::new(when)).then(|r| match r {

        Ok(r) => {

            println!("resolved in {}ms", r.elapsed_ms());

            r.result

        }

        _ => unreachable!(),

    });



    let mut runtime = Runtime::new().unwrap();

    runtime.block_on(f).unwrap();

}

How can I improve this and make it more idiomatic? Can I somehow get the interface to work similarly to inspect() or then()?

Delay::new(when)

  .timed(|res, elapsed| println!("{}ms!", elapsed))

  .and_then(...);

I tried creating a Timed trait and implementing it for Future but I didn't feel at all confident in how I was going about it. The types just really threw me for a loop.

Am I at least barking up the right tree?

The act of writing the future is easy enough, and adding a chainable method is the same technique as that shown in How can I add new methods to Iterator?.

The only really tricky aspect is deciding when the time starts — is it when the future is created or when it is first polled?

I chose to use when it's first polled, as that seems more useful:

extern crate futures; // 0.1.25

extern crate tokio; // 0.1.11



use std::time::{Duration, Instant};



use futures::{try_ready, Async, Future, Poll};

use tokio::{runtime::current_thread::Runtime, timer::Delay};



struct Timed<Fut, F>

where

    Fut: Future,

    F: FnMut(&Fut::Item, Duration),

{

    inner: Fut,

    f: F,

    start: Option<Instant>,

}



impl<Fut, F> Future for Timed<Fut, F>

where

    Fut: Future,

    F: FnMut(&Fut::Item, Duration),

{

    type Item = Fut::Item;

    type Error = Fut::Error;



    fn poll(&mut self) -> Poll<Self::Item, Self::Error> {

        let start = self.start.get_or_insert_with(Instant::now);



        let v = try_ready!(self.inner.poll());



        let elapsed = start.elapsed();

        (self.f)(&v, elapsed);



        Ok(Async::Ready(v))

    }

}



trait TimedExt: Sized + Future {

    fn timed<F>(self, f: F) -> Timed<Self, F>

    where

        F: FnMut(&Self::Item, Duration),

    {

        Timed {

            inner: self,

            f,

            start: None,

        }

    }

}



impl<F: Future> TimedExt for F {}



fn main() {

    let when = Instant::now() + Duration::from_millis(100);



    let f = Delay::new(when).timed(|res, elapsed| println!("{:?} elapsed, got {:?}", elapsed, res));



    let mut runtime = Runtime::new().unwrap();

    runtime.block_on(f).unwrap();

}